Opioid-dependent individuals with a history of abuse have exhibited worse mental and physical health compared to those without such a history; however, the evidence regarding the influence of abuse histories on addiction treatment outcomes are conflicting. In the present study, we identified history of physical or sexual abuse at treatment initiation in relation to drug use and health among long-term opioid-dependent individuals and we determined the relationship of abuse histories with treatment outcomes following substitution treatment. We analyzed data from a randomized controlled trial that compared the effectiveness of opioid-agonists in the treatment of chronic opioid dependence. The North American Opiate Medication Initiative (NAOMI) was conducted in Vancouver and Montreal (Canada) and provided oral methadone, injectable diacetylmorphine or injectable hydromorphone, the last two on a double blind basis, over 12months. A total of 112 (44.6%) participants reported a history of physical or sexual abuse at baseline. Participants with an abuse history reported a significantly higher number of chronic medical problems, suicide attempts, and previous drug treatments and had poorer psychiatric, family and social relations, and quality of life status compared to those without abuse histories. No differences in current and past substance use were found between those with and without abuse histories. Following 12months of treatment, the participants with abuse histories improved to a similar degree as those without a history of abuse in all of the European Addiction Severity Index sub-scales, with the exception of medical status. The findings suggest that individuals with abuse histories were able to achieve similar outcomes as those without abuse histories following treatment despite having poorer scores in physical and mental health, social status and quality of life at treatment initiation. These findings suggest that the substitution treatments as provided in this study can benefit the most vulnerable and access needs to be expanded to reach this population. Copyright (c) 2010 Elsevier Ltd. All rights reserved.